CVE-2005-0233 in Firefox
Summary
by MITRE
The International Domain Name (IDN) support in Firefox 1.0, Camino .8.5, and Mozilla before 1.7.6 allows remote attackers to spoof domain names using punycode encoded domain names that are decoded in URLs and SSL certificates in a way that uses homograph characters from other character sets, which facilitates phishing attacks.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 07/01/2019
The vulnerability described in CVE-2005-0233 represents a critical security flaw in the handling of international domain names within major web browsers including Firefox 1.0, Camino 0.8.5, and Mozilla versions prior to 1.7.6. This issue stems from the improper implementation of International Domain Name support which allows attackers to exploit the difference between Unicode and ASCII character representations in domain names. The core problem manifests when punycode encoded domain names are processed, where the system displays decoded Unicode characters in URLs and SSL certificates while the underlying encoded representation remains in the actual domain resolution process. This creates a scenario where attackers can register domain names using characters from different character sets that visually appear identical or nearly identical to legitimate domains, effectively creating homograph attacks.
The technical implementation flaw resides in how browsers handle the display and verification of domain names during SSL certificate validation and URL rendering processes. When a user visits a website, the browser displays the domain name in the address bar using Unicode characters that may be visually indistinguishable from legitimate domains, while the actual SSL certificate verification still operates on the encoded punycode representation. This discrepancy creates a window of opportunity for attackers to register domains that appear identical to well-known legitimate websites, such as using Cyrillic characters that look identical to Latin characters in the domain name. The vulnerability specifically affects the rendering and verification logic of domain names, where the display layer and the security verification layer operate with different character sets, leading to a mismatch that attackers can exploit for malicious purposes.
The operational impact of this vulnerability is severe and directly enables sophisticated phishing attacks that can bypass traditional security measures. Attackers can create domain names that visually appear identical to legitimate banking, e-commerce, or government websites, tricking users into entering sensitive information on fraudulent sites. The attack vector is particularly effective because users rely on visual recognition of domain names for security assessment, and the browsers' display mechanisms make it nearly impossible to distinguish between legitimate and malicious domains at first glance. This vulnerability undermines the fundamental security principle of domain name verification and can result in significant financial losses, identity theft, and corporate security breaches. The impact extends beyond individual users to enterprise environments where employees may inadvertently access malicious sites that appear legitimate due to the visual homograph characteristics.
The mitigation strategies for CVE-2005-0233 involve multiple layers of security improvements including updating browsers to versions that properly handle Unicode domain name rendering, implementing stricter domain name validation policies, and deploying security tools that can detect and block suspicious domain name patterns. Organizations should ensure all browsers are updated to versions that properly implement the Unicode domain name handling standards, which typically include displaying domain names in a consistent character set that prevents visual confusion. The vulnerability aligns with CWE-1004 which addresses insecure default settings in security-critical code, and relates to ATT&CK technique T1566 which covers phishing attacks through homograph domains. Security administrators should also consider implementing additional security measures such as DNS-based security solutions, web application firewalls, and user education programs that specifically address the risks of visual domain name spoofing attacks. The fundamental fix requires browser vendors to synchronize the display and verification layers of domain name handling to ensure that what users see in the address bar matches what the security verification system uses for certificate validation.